Method for controlling a hybrid drivetrain and battery device in the hybrid drivetrain

ABSTRACT

A method for controlling a hybrid drivetrain in a motor vehicle having an internal combustion engine, which has a crankshaft and an electric machine which can be operated as a motor and generator, having a rotor operatively connected to the crankshaft, having a torsional vibration damper operatively connected to the crankshaft, having a battery device for exchanging electrical energy with the electric machine, and having a control unit for controlling the battery device and the electric machine, and a corresponding battery device. To operate the electric machine with rapidly changing motor and generator operation without damaging the battery device, the electric machine is operatively connected to at least first and second electric batteries of the battery device, where at least part of the time one of the batteries is charged in the rhythm of occurring residual vibrations of the torsional vibration damper, while the other is discharged.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed under 35 U.S.C §120 and §365(c) as acontinuation of International Patent Application No. PCT/DE2012/000243filed Mar. 12, 2012, which application claims priority from GermanPatent Application No. 10 2011 016 012.4 tiled Apr. 4, 2011, whichapplications are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The invention relates to a method for controlling a hybrid drivetrain ina motor vehicle having an internal combustion engine, which has acrankshaft and an electric machine which can be operated as a motor anda. generator, having a rotor operatively connected to the crankshaft,having a torsional vibration damper operatively connected to thecrankshaft, having a battery device for exchanging electrical energywith the electric machine, and having a control unit for controlling thebattery device and the electric machine, and a corresponding batterydevice.

BACKGROUND OF THE INVENTION

Hybrid drivetrains are known from series applications in motor vehicles.These hybrid drivetrains employ, for example, an electric machine, whichserves as a starter for the combustion engine, as an additional orpart-time solitary drive, and for recovering the kinetic energy of themotor vehicle, as a motor and generator; the electric machine beingoperatively connected to a battery device, which stores and emitselectrical energy.

A device for reducing non-uniformities of rotation of a combustionengine is also known from German Patent No, 197 09 299 A1, wherehalf-waves from the electric machine switched to generator operationwhich lie above a mean torque of the combustion engine are damped andthe released energy is stored in the battery unit, and the electricmachine is driven to fill out half-waves lying below a mean torque,energy being taken from the battery device. All-in-all, the charging anddischarging currents which occur here at the battery device in therhythm of the non-uniformities of rotation of the combustion engine arehigh, so that the battery device may not have sufficient rechargingkinetics and is damaged in the course of time due to the recharging.

Furthermore, the non-uniformities of rotation, such as torsionalvibrations in modem combustion engines are so high, for example, due todownsizing and the like, that traditionally employed torsional vibrationdampers meet their capacity limits.

BRIEF SUMMARY OF THE INVENTION

The object of the invention is therefore to operate a hybrid drivetrainin such a way that, on the one hand, the torsional vibrations of thecombustion engine are damped in a satisfactory manner, and, on the otherhand, the battery device is spared. The object of the invention is alsoto design a corresponding battery device so that it has longer andbetter functionality, for example, with high-frequency rechargingprocesses between charging and discharging.

The object is fulfilled by a method for controlling a hybrid drivetrainin a motor vehicle, having an internal combustion engine, which has acrankshaft and an electric machine, which can be operated as a motor andgenerator, having a rotor operatively connected to the crankshaft,having a torsional vibration damper operatively connected to thecrankshaft, having a battery device for exchanging electrical energywith the electric machine, and having a control unit for controlling thebattery device and the electric machine, the electric machine beingoperatively connected to at least first and second electric batteries ofthe battery device, and at least part of the time being charged in therhythm of occurring residual vibrations of the torsional vibrationdamper of one of the batteries, while the other is being discharged. Forexample, to damp the residual vibrations of the torsional vibrationdamper through the alternating operation of the electric machine inmotor and generator mode, the recharging currents, which occur with highfrequency at the battery device, can be controlled such that one batteryis only charged and the other is only discharged. Such an operating modehelps to conserve the batteries in the battery device, therebyprolonging their service life.

To take account of a charge or discharge state of the batteries, thereis also a provision to switch them to a charging or discharging mode,independent of their charged condition, by the control unit, whosefunction may be provided in one or more physical control devices andcontrol units, in this connection, technically known devices, forexample, devices that are already present in the batteries in anadvantageous manner to determine the charged condition, can be conveyedto the control unit, which controls in particular the charging anddischarging currents for operating the electric machine which damps theresidual vibrations. It is understood that during the operating statesof the electric machine, for example, during the start, a recovery orthe like, both batteries may also be simultaneously charged ordischarged.

Furthermore, damping of the residual vibrations by means of the electricmachine may also be suspended if the charge state or operating conditionof the batteries falls below a specified residual charge or residualcapacity, for example, at very low temperatures, during long drives withthe support of the electric machine or the like.

In this connection, besides controlling the battery unit, the controlunit controls the electric machine, while the battery switched to thecharging state is charged by means of half-waves that lie above a meantorque of the residual vibrations, which are converted to electricalenergy by driving the electric machine, and the battery switched to thedischarging state drives the electric machine by half-waves that liebelow a mean torque of the residual vibrations to compensate. Theoperating data for controlling the electric machine and the batterydevice are provided by corresponding sensor devices for detectingrotational characteristics such as angles of rotation and their temporalderivatives from shafts such as the crankshaft of the combustion engine,the transmission input shaft(s) of a gear unit, the rotor shaft of theelectric machine, inner variables of the engine controller of thecombustion engine such as engine characteristics, upper dead-centerposition and the like.

The object is also fulfilled by a battery device for carrying out theproposed method in a hybrid drivetrain which has first and secondbatteries which are alternately connectible by means ofcurrent-direction-sensitive switches and a control unit for connectingthe switch, as well as a frequency converter. In this case, the minuspole is preferably grounded and the plus pole is connected by means ofthe switch, Alternatively, the grounding paths of the batteries can beconnected by means of the proposed switches. To this end, the controlunit issues a control signal in a preferred manner to two alternatelyswitching logic switches, which switch the switches themselves, where ina preferred embodiment a switch for the charging current and a switchfor the discharging current are provided at each plus pole, and theseare alternately switched contrary to each other. In order to damp theresidual vibrations of the torsional vibration damper, the switches areswitched alternately with reference to the batteries, so that only onebattery is charged and the other is discharged. If the electric machineis to start the combustion engine in motor mode or to deliver additionaldrive torque in a boost mode, the discharge switches of both batteriescan be switched and the charge switches deactivated. In the case ofrecovery with the motor vehicle in deceleration mode, on the other hand,the charge switches of both batteries can be switched and the dischargeswitches deactivated. It is understood that the connection layout of theswitches can be designed so that, for example, for simultaneousdischarging or simultaneous charging of both batteries the switches canbe switched accordingly, for example, the charge switches and thedischarge switches can be connected simultaneously.

In an embodiment of a battery device, devices may be provided in each ofthe batteries to ascertain the charge state, which have a signalconnection to the control unit and report the present charge state ofthe batteries, right down to individual charge states of the batterycells. The control unit registers the charge states and determines acharging plan for the various operating states of the motor vehicle, forexample, for damping the residual vibrations of the torsional vibrationdamper by means of the electric machine. The control unit registersand/or obtains for this purpose data for appraising the operatingstates, for example, starting the combustion engine, shifting thetransmission, compression and acceleration modes of the motor vehicleand the like.

The switches may be made, for example, of active electronic components,e.g., MOSFETs (metal-oxide-semiconductor field-effect transistors).However, IGBTs (insulated-gate bipolar transistors) have proven to beadvantageous, which, in contrast to MOSFETs, block completely againstthe switching direction due to the absence of suppressor diodes.

Lead storage batteries and the like may be used, for example, as thebatteries. However, lithium-ion batteries have proven advantageous dueto their favorable power-to-weight ratio and their time-dependentcharging and discharging behavior. Connecting the latter by means of theswitches prevents damage, which can occur, for example, due tosubjecting them to micro-cycles, as are necessary when damping residualvibrations by means of the electric machine, Due to the currents thatare directed through the converter and the switches into thecorresponding battery in only one direction of flow, long chargingcycles are produced, which can he set as macro-cycles for each battery,from a low charge state up to a prescribed charge state. When thebatteries are designed with the same capacity, each battery may becharged alternately to approximately the maximum capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature and mode of operation of the present invention will now bemore fully described in the following detailed description of theinvention taken with the accompanying drawing figures, in which:

FIG. 1 is a circuit diagram for controlling the charge states ofbatteries of a. battery device;

FIG. 2 is a depiction of charging processes of a conventional batterydevice having a battery and the battery device of the present invention,over time;

FIG. 3 is a depiction of the currents appearing in a hybrid drivetrainduring a compensation of residual vibrations of a torsional vibrationdamper at a conventional battery device and the battery device of thepresent invention, over time; and,

FIG. 4 is a circuit diagram similar to the circuit diagram of Figure Ifor controlling the charge state of batteries of a battery device.

DETAILED DESCRIPTION OF THE INVENTION

At the outset, it should be appreciated that like drawing numbers ondifferent drawing views identify identical, or functionally similar,structural elements of the invention. While the present invention isdescribed with respect to what is presently considered to be thepreferred aspects, it is to be understood that the invention as claimedis not limited to the disclosed aspects.

Furthermore, it is understood that this invention is not limited to theparticular methodology, materials and modifications described and, assuch, may, of course, vary. it is also understood that the terminologyused herein is for the purpose of describing particular aspects only,and is not intended to limit the scope of the present invention, whichis limited only by the appended claims.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this invention belongs. Although any methods, devicesor materials similar or equivalent to those described herein can be usedin the practice or testing of the invention, the preferred methods,devices, and materials are now described.

FIG. 1 shows circuit diagram 2 of battery device 1, having first andsecond batteries 3, 4 with the same or different capacity, control unit5 and converter 6, which are connected to each other by means ofgrounding line 7. Converter 6 forms the interface to the electricmachine (not shown), and transforms the direct current of batteries 3, 4into a plurality of alternating current phases, of which only one phasew is depicted here symbolically, to drive the electric machine,

Situated between converter 6 and batteries 3, 4 in each case are twoparallel-switched switches 8, 9, 10, 11 in the form of IGBTs connectedoppositely in regard to their switch position, so that with gates ofswitches 8, 9, 10. 11 connected in each case with the same signal levelthrough logic switches 12, 13, in each case one switch of battery 3, 4is switched to conductive and the other to non-conductive. in this case,the gates are connected so that, for example, at battery 3, when apositive level is present at output Out1 of control unit 5, switch 8 ofbattery 3 and switch 11 of battery 4 are switched so that when an ACsignal is present at access line 14 only battery 3 receives chargingCurrent through dosed switch 8, while switch 10 which is responsible forthe charging current of battery 4 remains open. In regard to dischargecurrent, switch 9 of battery 3 is open, and a discharge current is ableto flow from battery 4 through closed switch 11.

If the level at output Out1 is set to Low, inversely switched logicswitches 12, 13 issue a level to the gates of switches 9, 10, so thatthe discharge current from battery 3 and the charge current for battery4 are switched through switch 9, while switches 8, 11 remain open.

The connection of output Out! of control unit 5 is dependent on thecharge states ascertained in batteries 3, 4 by devices 15, 16, which aremade up of the charge states of the individual cells and are fed toinputs In1, In2 of control unit 5 by means of signal lines 17, 18.

FIG. 2 shows Diagram 19, in which curves 20, 21, 22 represent the chargestates of batteries against time in the range of, for example, severalminutes to several hours, where these charge states may vary and dependamong other things on the capacity of the batteries and their electrodekinetics. The actual excitations of the drivetrain, which the torsionalvibration damper in the drivetrain does not damp adequately, cause smallwaves in the range of approximately 100 Hz in the DC section which isdownline from the converter. The depiction of the long-term chargingprocess and the depiction of the AC portion of the excitations are shownoverdrawn in Diagram 19 to explain the effects.

Curve 22, identified using the symbols ‘+,’ shows a conventional batterydevice having a charge state of approximately 30% during a compensationof residual vibrations of a torsional vibration damper by means of anelectric machine, which is connected to the single battery of thebattery device. The battery is charged and discharged here usingmicro-cycles, which may lie within the range of the frequency of theoccurring residual vibrations of the torsional vibration damper. Thebattery may be damaged by such micro-cycles and have a short servicelife.

Curves 20, 21, identified using the symbols ‘o’ and ‘x’ respectively,show the charge states of battery device 1 of FIG. 1, first and secondbatteries 3, 4 having different capacities—as is evident from FIG. 2.The connection of batteries 3, 4 in accordance with circuit diagram 2results in the uniform charging and discharging of the batteries overmacro-cycles, which can be made to approximate the charging anddischarging processes recommended. by the manufacturer. In this case,the battery with curve 20 has the smaller capacity, so that itdetermines the macro-cycles, which may range from a few minutes to a fewhours in length. The charge states are measured at the batteries and areregistered by control unit 5, which controls the switching of switches8, 9, 10, 11 to adjust the macro-cycles. In one embodiment, the batterywith curve 20 is charged up to a charge state of 80% of the totalcapacity and discharged to 20% thereof, which results in a recharging ofbetween 20% and 32% of its total capacity for the battery having thegreater capacity.

FIG. 3 shows Diagram 23, with currents occurring cyclically at batterydevices during the compensation of residual vibrations of a torsionalvibration damper by means of an electric machine connected to thebatteries of the battery devices, over time. Here curve 24, identifiedusing the symbols ‘x,’ shows the currents of a conventional batterydevice having a single battery, which is recharged micro-cyclically atthe frequency of the alternating currents. The batteries connected inaccordance with circuit diagram 2 of FIG. 1, on the other hand, are onlycharged or discharged, so that over a relatively long macro-cycle theyundergo only positive or negative current cycles, as may be seen fromcurves 25, 26 identified using the symbols ‘o’ and respectively, whicheach show the current of one battery.

FIG. 4 shows circuit diagram 2 a of first and second batteries 3 a, 4 awith the same or different capacity, control unit 5 a and converter 6 a,which are connected to each other by means of grounding line 7 a andaccess line 14 a. Converter 6 a forms the interface to electric machine27, and converts the DC current of batteries 3 a, 4 a to a plurality ofAC phases u, v, w to drive electric machine 27. At the same time,phase-selective commutation currents or commutation voltages in therange from 100 Hz to 1 kHz are output, while the voltage modulationsrecovered by electric machine 27 to damp the vibration of thedrivetrain, which are transmitted via converter 6 a to the DC network,i.e., via access line Ha and grounding line 7 a to the batteries, liewithin the range from approximately 60 to 100 Hz. Switches 8 a, 9 a, 10a, Ha. are addressed directly by control unit 5 a by means of controllines 28, 29, 30, 31, and are thereby placed in a through-connected oropen state.

Because of the free design of the connection of switches 8 a, 9 a, 10 a,11 a by control unit 5 a, one of batteries 3 a, 4 a can be charged whilethe other is being discharged. To this end, for example, switch 8 a isconnected through in the direction of battery 3 a and switch Ha isconnected through in the direction of converter 6 a, while switches 9 a,10 a are open. This causes battery 3 a to be charged and battery 4 a tobe discharged. By closing switches 8 a, 10 a in the same direction, bothbatteries 3 a, 4 a are charged, for example, during recovery of thedrivetrain while the motor vehicle is decelerating, and by closingswitches 9 a, 11 a in the same direction both batteries 3 a, 4 a aredischarged simultaneously, for example, while starting the combustionengine or when the drivetrain is in boost mode.

Control unit 5 a has a signal connection to batteries 3 a, 4 a andconverter 6 a by means of signal lines 17 a, 18 a, 32, and therebycontrols the charging of the batteries and the commutation of electricmachine 27.

Thus, it is seen that the objects of the present invention areefficiently obtained, although modifications and changes to theinvention should be readily apparent to those having ordinary skill inthe art, which modifications are intended to be within the spirit andscope of the invention as claimed. It also is understood that theforegoing description is illustrative of the present invention andshould not be considered as limiting. Therefore, other embodiments ofthe present invention are possible without departing from the spirit andscope of the present invention.

LIST OF REFERENCE NUMBERS

-   1 battery device-   2 circuit diagram-   2 a circuit diagram-   3 battery-   3 a battery-   4 battery-   4 a battery-   5 control unit-   5 a control unit-   6 converter-   6 a. converter-   7 grounding line-   7 a grounding line-   8 switch-   8 a switch-   9 switch-   9 a. switch-   10 switch-   10 a switch-   11 switch-   11 a switch-   12 logic switch-   13 logic switch-   14 access line-   14 a access line-   15 device-   16 device-   17 signal line-   17 a signal line-   18 signal line-   18 a signal line-   19 diagram-   20 curve-   21 curve-   22 curve-   23 diagram-   24 curve-   25 curve-   26 curve-   27 electric machine-   28 control line-   29 control line-   30 control line-   31 control line-   32 signal line-   In1 input-   In2 input-   Out1 output-   u phase-   v phase-   w phase

What is claimed is:
 1. A method for controlling a hybrid drivetrain in amotor vehicle having an internal combustion engine, which has acrankshaft and an electric machine which can be operated as a motor andgenerator, having a rotor operatively connected to the crankshaft,having a torsional vibration damper operatively connected to thecrankshaft, having a battery device for exchanging electrical energywith the electric machine, and having a control unit for controlling thebattery device and the electric machine, the method comprising thefollowing steps: operatively connecting the electric machine to at leastfirst and second electric batteries of the battery device; and, chargingthe first hatter, using the electric machine, in the rhythm of occurringresidual vibrations of the torsional vibration damper, while the secondbattery is being discharged.
 2. The method as recited in claim 1,wherein the batteries are switched by the control unit to a charging ordischarging state, depending on their charge condition.
 3. The method asrecited in claim 2, wherein the battery switched to the charging stateis charged by means of half-waves that lie above a mean torque of theresidual vibrations, which are converted to electrical energy by drivingthe electric machine, and the battery switched to the discharging statedrives the electric machine in phases of half-waves that lie below a.mean torque of the residual vibrations to compensate.
 4. A batterydevice for carrying out the method as recited in claim 1, comprising:first and second batteries which can be connected by means of aplurality of current-direction-sensitive switches and a control unit forcontrolling the switches, as well as a converter.
 5. The battery deviceas recited in claim 4, wherein in each of the batteries a devicedetermines the charge condition, which has a signal connection to thecontrol unit.
 6. The battery device as recited in claim 4, wherein eachbattery has a switch for charging and discharging, and the switches canbe operated alternately by the control unit,
 7. The battery device asrecited in claim 4, wherein the switches are bipolar transistors havinginsulated gate electrodes, switched by the control unit.
 8. The batterydevice as recited in claim 7, wherein an inverting logic switch issituated between each switch and an output of the control unit, and theother two switches are connected directly to an output.
 9. The batterydevice as recited in claim 1, wherein the switches can be addressedindividually by the control unit to control them.
 10. The battery deviceas recited in claim 4, wherein the batteries are lithium-ion batteries.11. The battery device as recited in claim 4, wherein the batteries havedifferent capacities.